1. Field of the Invention
The present invention relates to an exhaust gas recirculation valve provided in an exhaust gas recirculation passage of an exhaust gas recirculation apparatus and to be driven by an actuator to open and close.
2. Related Art
As a technique of the above type, there is conventionally known an exhaust gas recirculation valve (EGR valve) disclosed in for example JP 2008-202516A. In a housing of this EGR valve, a valve stem is provided to be movable through a bearing so that the valve stem is moved reciprocally (stroke movement) by an actuator to operate a valve element to open and close with respect to a valve seat. To be concrete, the valve stem is formed, in its one end portion, with male screw threads and the actuator is formed with female screw threads engaging with the male screw threads. The actuator is driven to cause screw motion of the male screw threads with respect to the female screw threads, thereby making stroke movement of the valve stem to open and close the valve element with respect to the valve seat. Accordingly, the gas flow characteristics of the EGR valve are defined by the shapes of the valve element and the valve seat. Due to this configuration, it is impossible to set gas flow characteristics extremely different between a low opening range and a high opening range.